feat(config): add --default flag to config-get for graceful absent-key handling (#1893) (#1920)

When --default <value> is passed, config-get returns the default value
(exit 0) instead of erroring (exit 1) when the key is absent or
config.json doesn't exist. When the key IS present, --default is
ignored and the real value returned.

This lets workflows express optional config reads without defensive
`2>/dev/null || true` boilerplate that obscures intent and is fragile
under `set -e`.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/config-get-default.test.cjs

@@ -0,0 +1,110 @@
+/**
+ * Tests for config-get --default flag (#1893)
+ *
+ * When --default <value> is passed, config-get should return the default
+ * value (exit 0) instead of erroring (exit 1) when the key is absent.
+ * When the key IS present, --default should be ignored and the real value
+ * returned.
+ */
+
+'use strict';
+
+const { describe, test, beforeEach, afterEach } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('fs');
+const path = require('path');
+const { execFileSync } = require('child_process');
+const os = require('os');
+
+const GSD_TOOLS = path.join(__dirname, '..', 'get-shit-done', 'bin', 'gsd-tools.cjs');
+
+describe('config-get --default flag (#1893)', () => {
+  let tmpDir;
+  let planningDir;
+
+  beforeEach(() => {
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'gsd-config-default-'));
+    planningDir = path.join(tmpDir, '.planning');
+    fs.mkdirSync(planningDir, { recursive: true });
+  });
+
+  afterEach(() => {
+    fs.rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  function run(...args) {
+    return execFileSync('node', [GSD_TOOLS, ...args, '--cwd', tmpDir], {
+      encoding: 'utf-8',
+      timeout: 5000,
+    }).trim();
+  }
+
+  function runRaw(...args) {
+    return run(...args, '--raw');
+  }
+
+  function runExpectError(...args) {
+    try {
+      execFileSync('node', [GSD_TOOLS, ...args, '--cwd', tmpDir], {
+        encoding: 'utf-8',
+        timeout: 5000,
+        stdio: ['pipe', 'pipe', 'pipe'],
+      });
+      assert.fail('Expected command to exit non-zero');
+    } catch (err) {
+      assert.ok(err.status !== 0, 'Expected non-zero exit code');
+      return err;
+    }
+  }
+
+  test('absent key without --default errors', () => {
+    fs.writeFileSync(path.join(planningDir, 'config.json'), '{}');
+    runExpectError('config-get', 'nonexistent.key', '--raw');
+  });
+
+  test('absent key with --default returns default value', () => {
+    fs.writeFileSync(path.join(planningDir, 'config.json'), '{}');
+    const result = runRaw('config-get', 'nonexistent.key', '--default', 'fallback');
+    assert.equal(result, 'fallback');
+  });
+
+  test('absent key with --default "" returns empty string', () => {
+    fs.writeFileSync(path.join(planningDir, 'config.json'), '{}');
+    const result = runRaw('config-get', 'nonexistent.key', '--default', '');
+    assert.equal(result, '');
+  });
+
+  test('present key with --default returns real value (ignores default)', () => {
+    fs.writeFileSync(path.join(planningDir, 'config.json'), JSON.stringify({
+      workflow: { discuss_mode: 'adaptive' }
+    }));
+    const result = runRaw('config-get', 'workflow.discuss_mode', '--default', 'ignored');
+    assert.equal(result, 'adaptive');
+  });
+
+  test('nested absent key with --default returns default', () => {
+    fs.writeFileSync(path.join(planningDir, 'config.json'), JSON.stringify({
+      workflow: {}
+    }));
+    const result = runRaw('config-get', 'workflow.deep.missing.key', '--default', 'safe');
+    assert.equal(result, 'safe');
+  });
+
+  test('missing config.json with --default returns default', () => {
+    // No config.json written
+    const result = runRaw('config-get', 'any.key', '--default', 'no-config');
+    assert.equal(result, 'no-config');
+  });
+
+  test('missing config.json without --default errors', () => {
+    // No config.json written
+    runExpectError('config-get', 'any.key', '--raw');
+  });
+
+  test('--default works with JSON output (no --raw)', () => {
+    fs.writeFileSync(path.join(planningDir, 'config.json'), '{}');
+    const result = run('config-get', 'missing.key', '--default', 'json-test');
+    const parsed = JSON.parse(result);
+    assert.equal(parsed, 'json-test');
+  });
+});